The overall objective of the proposed research is to study the extent to which neural pathways contribute to the control of body salt and water. Experiments will be carried out in which measurements will be made of the electrical activity of fibers originating from the heart and kidney with particular reference to type B atrial fibers which are believed to sense the distension and thus volume of the atrium. The electrophysiologic measrements will be correlated with various hemodynamic measurements including dynamic atrial pressure and renal function. Particular attention will be given to the possibility that afferent neural pathways may play a role in the very early response to volume expansion but a minor role under conditions of long term volume expansion. These experiments will provide further information concerning the extent to which the heart and kidney can sense directly or indirectly alterations in intravascular volume.